(57) A pitch control mechanism is provided for angular displacement of propellers of a
propeller assembly of an engine arrangement. The pitch control mechanism has an epicyclic
gear system rotating with the propeller assembly. The epicyclic gear system comprises
a sun gear (18), one or more planet gears (19) engaging the sun gear (18), a ring
gear (20) engaging the planet gears, and a planet carrier carrying the planet gears.
One of the sun gear (18), the ring gear (20) and the planet carrier is a first input
to the epicyclic gear system. Another of the sun gear (18), the ring gear (19) and
the planet carrier is a second input to the epicyclic gear system. The last of the
sun gear (18), the ring gear (19) and the planet carrier is an output from the epicyclic
gear system. The pitch control mechanism further has a drive gear located on a static
structure of the engine arrangement, and controlling the rotational speed of the first
epicyclic input in the rotating frame of reference of the propeller assembly. The
pitch control mechanism further has a control gear (32) located on a static structure
of the engine arrangement, and controlling the rotational speed of the second epicyclic
input in the rotating frame of reference of the propeller assembly. The pitch control
mechanism further has a drive mechanism (31) rotating with the propeller assembly.
The drive mechanism (31) accepts rotary motion from the epicyclic output to deliver
an output motion which angularly displaces the propellers (22a,22b) of the propeller
assembly. Varying a rotation of at least one of the drive gear (31) and the control
gear (32) varies the direction of rotation of the epicyclic output. This changes the
output motion delivered by the drive mechanism to control the angular displacement
of the propellers of the propeller assembly.
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